Force management system that includes a force measurement assembly, a visual display device, and one or more data processing devices

ABSTRACT

A force measurement system includes a force measurement assembly with a top surface configured to receive at least one portion of the body of a subject and at least one force transducer configured to sense forces and/or moments being applied to the top surface; at least one visual display device having an output screen configured to at least partially circumscribe three sides of a torso of the subject, and one or more data processing devices operatively coupled to the force measurement assembly and the at least one visual display device. In one or more embodiments, the force measurement assembly may be in the form of an instrumented treadmill. In one or more further embodiments, the force measurement system may additionally comprise a motion capture system configured to detect the motion of one or more body gestures of the subject.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. Nonprovisional patent applicationSer. No. 15/242,558 entitled “Force Measurement System That Includes AForce Measurement Assembly, A Visual Display Device, And One Or MoreData Processing Devices”, filed on Aug. 21, 2016, and further claims thebenefit of U.S. Provisional Patent Application No. 62/208,671, entitled“Force Measurement System”, filed on Aug. 22, 2015, the disclosure ofeach of which is hereby incorporated by reference as if set forth intheir entirety herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable.

INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISK

Not Applicable.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention generally relates to force measurement systems. Moreparticularly, the invention relates to a force measurement system thatis capable of immersing a subject in a virtual reality environment.

2. Background and Description of Related Art

Force measurement systems are utilized in various fields to quantify thereaction forces and moments exchanged between a body and supportsurface. For example, in biomedical applications, force measurementsystems are used for gait analysis, assessing balance and mobility,evaluating sports performance, and assessing ergonomics. In order toquantify the forces and moments resulting from the body disposedthereon, the force measurement system includes some type of forcemeasurement device. Depending on the particular application, the forcemeasurement device may take the form of a balance plate, force plate,jump plate, a force plate array, or some other device that is capable ofquantifying the forces and moments exchanged between the body and thesupport surface.

Although, it is often difficult to accommodate conventional forcemeasurement systems in the spaces of many buildings due to theirexpansive sizes. For example, a force plate array, which is often usedas part of a gait lab in a building, typically occupies a considerableamount of floor space in the building. In addition to the difficultiesassociated with the space requirements for these systems, conventionalforce measurement systems are not capable of effectively immersing thesubject being tested in a virtual reality environment, which may be usedto simulate real-life scenarios that are encountered by the subject.

Therefore, what is needed is a force measurement system that includes animmersive visual display device that enables a subject being tested tobecome fully immersed in a virtual reality scenario or an interactivegame. In addition, what is needed is a force measurement system that iscapable of fully immersing a subject in a virtual reality environment,yet compact enough to fit in typical building spaces.

BRIEF SUMMARY OF EMBODIMENTS OF THE INVENTION

Accordingly, the present invention is directed to a force measurementsystem that substantially obviates one or more problems resulting fromthe limitations and deficiencies of the related art.

In accordance with one or more embodiments of the present invention,there is provided a force measurement system comprising a forcemeasurement assembly configured to receive a subject, the forcemeasurement assembly including a top surface for receiving at least oneportion of the body of the subject; and at least one force transducer,the at least one force transducer configured to sense one or moremeasured quantities and output one or more signals that arerepresentative of forces and/or moments being applied to the top surfaceof the force measurement assembly by the subject; at least one visualdisplay device having an output screen configured to at least partiallycircumscribe three sides of a torso of the subject, the at least onevisual display device configured to display one or more scenes on theoutput screen so that the scenes are viewable by the subject, whereinthe one or more scenes are configured to create a simulated environmentfor the subject, and wherein the output screen of the at least onevisual display device comprises a bottom edge and a top edge; and one ormore data processing devices operatively coupled to the forcemeasurement assembly and the at least one visual display device, the oneor more data processing devices configured to receive the one or moresignals that are representative of the forces and/or moments beingapplied to the top surface of the force measurement assembly by thesubject, and to convert the one or more signals into output forcesand/or moments, the one or more data processing devices furtherconfigured to dynamically increase or decrease a speed of one or moredisplaceable components of the force measurement system in accordancewith a visual element of the one or more scenes that are displayed onthe output screen of the at least one visual display device while thesubject navigates through the one or more scenes of the simulatedenvironment on the output screen of the at least one visual displaydevice.

In a further embodiment of the present invention, the at least onevisual display device comprises a concavely shaped projection screenhaving a cylindrical middle portion, a spherical bottom portion, and aspherical top portion, the cylindrical middle portion being disposedabove the spherical bottom portion and below the spherical top portion,the cylindrical middle portion having a continuous curvature betweenfirst and second opposed side edges of the concavely shaped projectionscreen, wherein the cylindrical middle portion of the concavely shapedprojection screen results in a focal region for a subject disposed onthe force measurement assembly, rather than any one single focal point,so that an immersion experience for the subject is substantiallyunaffected by a height of the subject.

In yet a further embodiment, the concavely shaped projection screencomprises a plurality of screen sections that are attached to oneanother so as to form the overall screen.

In still a further embodiment, the force measurement assembly is in theform of an instrumented treadmill.

In yet a further embodiment, the force measurement system furthercomprises a motion base disposed underneath the instrumented treadmill,the motion base configured to displace the instrumented treadmill in oneor more directions.

In still a further embodiment, the output screen of the at least onevisual display device further comprises an overhanging top portion and atop cutout defining a cutout footprint; and the force measurement systemfurther comprises a motion capture system operatively coupled to the oneor more data processing devices, the motion capture system comprising atleast one motion capture device configured to detect the motion of oneor more body gestures of the subject, and the at least one motioncapture device being disposed within the cutout footprint of the topcutout of the output screen of the at least one visual display device.

In yet a further embodiment, the at least one motion capture devicecomprises a plurality of motion capture devices, a subset of theplurality of motion capture devices being circumferentially spaced apartaround the top cutout of the output screen of the at least one visualdisplay device, and the subset of the plurality of motion capturedevices being disposed within the cutout footprint.

In still a further embodiment, the one or more data processing devicesare configured to adjust the one or more scenes on the output screen ofthe at least one visual display device in accordance with the detectedmotion of the one or more body gestures of the subject by the at leastone motion capture device, wherein the one or more body gestures of thesubject comprise at least one of: (i) one or more limb movements of thesubject, (ii) one or more torso movements of the subject, and (iii) acombination of one or more limb movements and one or more torsomovements of the subject.

In yet a further embodiment, the at least one motion capture devicecomprises a plurality of motion capture devices, and the plurality ofmotion capture devices of the motion capture system are in the form of aplurality of cameras, the plurality of cameras configured to capture themotion of the subject.

In still a further embodiment, a first subset of the plurality ofcameras of the motion capture system are disposed above the subject, andwherein a second subset of the plurality of cameras of the motioncapture system are disposed behind the subject.

In yet a further embodiment, the first subset of the plurality ofcameras of the motion capture system are attached to the output screenof the at least one visual display device or to a screen supportstructure that supports the output screen of the at least one visualdisplay device; and the second subset of the plurality of cameras of themotion capture system are attached to one of: (i) the output screen ofthe at least one visual display device, (ii) a screen support structurethat supports the output screen of the at least one visual displaydevice, and (iii) a camera mounting structure that is attached to theoutput screen of the at least one visual display device or to the screensupport structure.

In still a further embodiment, the top surface of the force measurementassembly is disposed above the bottom edge of the output screen of theat least one visual display device, and the bottom edge of the outputscreen of the at least one visual display device is spaced apart from afloor on which the at least one visual display device is supported byone or more screen support members, the one or more screen supportmembers being spaced apart from the top surface of the force measurementassembly that is configured to receive the at least one portion of thebody of the subject.

In yet a further embodiment, the force measurement system furthercomprises an input device operatively coupled to the one or more dataprocessing devices, the input device configured to enable the subject toselect different navigation paths in the one or more scenes of thesimulated environment on the output screen of the at least one visualdisplay device.

In still a further embodiment, the input device that is configured toenable the subject to select different navigation paths in the one ormore scenes of the simulated environment on the output screen of the atleast one visual display device comprises an eye position trackingdevice or a head position tracking device.

In accordance with one or more other embodiments of the presentinvention, there is provided a force measurement system comprising aforce measurement assembly configured to receive a subject, the forcemeasurement assembly including one or more displaceable components, theone or more displaceable components having one or more respectivesurfaces for receiving one or more respective limbs of the subject; andat least one force transducer, the at least one force transducerconfigured to sense one or more measured quantities and output one ormore signals that are representative of one or more loads being appliedto the one or more respective surfaces of the one or more displaceablecomponents by the subject; at least one visual display device having anoutput screen, the at least one visual display device configured todisplay a scene on the output screen so that the scene is viewable bythe subject; a pointing or gaze direction determination deviceconfigured to determine a pointing direction or gaze direction of thesubject, the pointing or gaze direction determination device beingexternal to the at least one visual display device; and one or more dataprocessing devices operatively coupled to the at least one forcetransducer of the force measurement assembly, the at least one visualdisplay device, and the pointing or gaze direction determination device,the one or more data processing devices configured to receive the one ormore signals that are representative of the forces and/or moments beingapplied to the one or more respective surfaces of the one or moredisplaceable components by the subject, and to convert the one or moresignals into output forces and/or moments, the one or more dataprocessing devices further configured to generate at least a firstvisual element and a second visual element, and to display the firstvisual element and the second visual element in the scene on the outputscreen of the at least one visual display device, the one or more dataprocessing devices additionally configured to control the displacementof the one or more displaceable components of the force measurementassembly in accordance with the first visual element of the scene thatis displayed on the output screen of the at least one visual displaydevice, the one or more data processing devices further configured todetermine a manner in which the subject interacts with the second visualelement of the scene and to adjust the displacement of the one or moredisplaceable components of the force measurement assembly based upon theinteraction of the subject with the second visual element during asubject testing or training routine, the second visual element of thescene that is displayed on the output screen of the at least one visualdisplay device comprising at least one virtual target, and the one ormore data processing devices additionally configured to determine themanner in which the subject interacts with the second visual element ofthe scene by determining when the pointing direction or the gazedirection of the subject, as determined by the pointing or gazedirection determination device, coincides with the at least one virtualtarget displayed on the output screen, and when the pointing directionof the subject does not coincide with the at least one virtual targetdisplayed on the output screen. In these one or more other embodiments,when the pointing direction of the subject coincides with the at leastone virtual target displayed on the output screen during the subjecttesting or training routine, the one or more data processing devices arefurther configured to maintain a current speed of the one or moredisplaceable components of the force measurement assembly. Also, inthese one or more other embodiments, when the pointing direction of thesubject does not coincide with the at least one virtual target displayedon the output screen during the subject testing or training routine, theone or more data processing devices are further configured to decreasethe speed of the one or more displaceable components of the forcemeasurement assembly below the current speed of the one or moredisplaceable components of the force measurement assembly so as to makeit easier for the subject to properly focus on the at least one virtualtarget during the subject testing or training routine.

In a further embodiment of the present invention, the force measurementassembly is disposed on a motion base, the motion base configured todisplace the force measurement assembly in one or more directions.

In yet a further embodiment, the force measurement assembly is in theform of an instrumented treadmill and the one or more displaceablecomponents are in form of one or more treadmill displaceable elements ofthe instrumented treadmill; and the one or more data processing devicesare further configured to adjust a rotational speed of the one or moretreadmill displaceable elements in accordance with the first visualelement of the scene that is displayed on the output screen of the atleast one visual display device.

In still a further embodiment, the first visual element of the scenethat is displayed on the output screen of the at least one visualdisplay device comprises a ground surface element; and the one or moredata processing devices are further configured to dynamically increaseor decrease the rotational speed of the one or more treadmilldisplaceable elements in accordance with a type of the ground surfaceelement of the scene that is displayed on the output screen of the atleast one visual display device.

In yet a further embodiment, the first visual element of the scene thatis displayed on the output screen of the at least one visual displaydevice comprises an obstacle disposed in a virtual walking path of thesubject; and the one or more data processing devices are furtherconfigured to dynamically decrease the rotational speed of the one ormore treadmill displaceable elements when a virtual representation ofthe subject on the output screen collides with the obstacle disposed inthe virtual walking path of the scene that is displayed on the outputscreen of the at least one visual display device.

In still a further embodiment, the virtual representation of the subjecton the output screen of the at least one visual display device comprisesan avatar controlled by one or more body gestures of the subject asdetected by the force measurement assembly and a motion detectionsystem.

In yet a further embodiment, the one or more data processing devices arefurther configured to compute a center of pressure for the subject as afunction of the output forces and/or moments determined from the one ormore signals of the force measurement assembly, and to control amovement of the virtual representation of the subject on the outputscreen of the at least one visual display device using the computedcenter of pressure.

In still a further embodiment, the pointing or gaze directiondetermination device comprises at least one of the following devices:(i) an eye position tracking device configured to track a position ofone or more eyes of the subject, (ii) a head position tracking deviceconfigured to track a position of the head of the subject, and (iii) apointing device configured to indicate an aiming direction of a bodyportion of the subject.

In yet a further embodiment, the one or more data processing devices arefurther configured to control a navigation of a virtual representationof the subject on the output screen of the at least one visual displaydevice in accordance with an output signal from at least one of the eyeposition tracking device, the head position tracking device, and thepointing device.

In still a further embodiment, the at least one virtual target that isgenerated by the one or more data processing devices and displayed onthe output screen of the at least one visual display device comprises aplurality of targets spaced apart on the output screen of the at leastone visual display device; and the one or more data processing devicesare further configured to determine whether the subject sequentiallypoints in respective directions of each of the plurality of targets.

In yet a further embodiment, during the subject testing or trainingroutine, when the pointing direction of the subject coincides with theat least one virtual target displayed on the output screen, the one ormore data processing devices are further configured to set a targetfocus variable to a first value. In this further embodiment, during thesubject testing or training routine, when the pointing direction of thesubject does not coincide with the at least one virtual target displayedon the output screen, the one or more data processing devices arefurther configured to set the target focus variable to a second valuethat is different from the first value. Also, in this furtherembodiment, the one or more data processing devices are furtherconfigured to maintain the current speed of the one or more displaceablecomponents of the force measurement assembly when the target focusvariable equals the first value, and the one or more data processingdevices are further configured to decrease the speed of the one or moredisplaceable components of the force measurement assembly below thecurrent speed of the one or more displaceable components of the forcemeasurement assembly when the target focus variable equals the secondvalue.

It is to be understood that the foregoing general description and thefollowing detailed description of the present invention are merelyexemplary and explanatory in nature. As such, the foregoing generaldescription and the following detailed description of the inventionshould not be construed to limit the scope of the appended claims in anysense.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention will now be described, by way of example, with referenceto the accompanying drawings, in which:

FIG. 1 is a perspective view of a force measurement system with a forcemeasurement assembly in the form of an instrumented treadmill, accordingto a first embodiment of the invention;

FIG. 2 is a front view of the force measurement system of FIG. 1;

FIG. 3 is a top view of the force measurement system of FIG. 1;

FIG. 4 is a side view of the force measurement system of FIG. 1;

FIG. 5 is a perspective view of a force measurement system with a forcemeasurement assembly in the form of an instrumented treadmill, accordingto a second embodiment of the invention;

FIG. 6 is a front view of the force measurement system of FIG. 5;

FIG. 7 is a perspective view of a concave projection screen of the forcemeasurement systems of FIGS. 1 and 5;

FIG. 8 is a longitudinal sectional view of the concave projection screenof FIG. 7;

FIG. 9 is a block diagram of constituent components of the forcemeasurement system with a force measurement assembly in the form of aninstrumented treadmill, according to an embodiment of the invention;

FIG. 10 is a block diagram of the software and hardware architecture ofthe force measurement system with the force measurement assembly in theform of the instrumented treadmill;

FIG. 11 is a screen image of an immersive grocery aisle scene displayedon the output screen of the visual display device of the forcemeasurement system, according to an embodiment of the invention;

FIG. 12 is another screen image of the immersive grocery aisle scene ofFIG. 11;

FIG. 13 is a screen image of an immersive island pathway scene displayedon the output screen of the visual display device of the forcemeasurement system, according to another embodiment of the invention,wherein a first type of pathway ground surface is illustrated;

FIG. 14 is another screen image of the immersive island pathway scene ofFIG. 13, wherein a second type of pathway ground surface is illustrated;

FIG. 15 is yet another screen image of the immersive island pathwayscene of FIG. 13, wherein a third type of pathway ground surface isillustrated;

FIG. 16 is yet another screen image of the immersive island pathwayscene of FIG. 13, wherein a portion of the pathway has a puddle of waterdisposed thereon;

FIG. 17 is a screen image of an immersive castle scene displayed on theoutput screen of the visual display device of the force measurementsystem, according to yet another embodiment of the invention;

FIG. 18 is another screen image of the immersive castle scene of FIG.17, wherein a target is provided in the bottom, left-hand corner of thescreen;

FIG. 19 is yet another screen image of the immersive castle scene ofFIG. 17, wherein a target is provided in the bottom, right-hand cornerof the screen;

FIG. 20 is still another screen image of the immersive castle scene ofFIG. 17, wherein a target is provided in the top, left-hand corner ofthe screen;

FIG. 21 is yet another screen image of the immersive castle scene ofFIG. 17, wherein a target is provided in the top, right-hand corner ofthe screen;

FIG. 22 is still another screen image of the immersive castle scene ofFIG. 17, wherein two spaced-apart targets are provided at the top of thescreen; and

FIG. 23 is yet another screen image of the immersive castle scene ofFIG. 17, wherein two targets are provided in oppositely disposed top andbottom corners of the screen.

Throughout the figures, the same parts are always denoted using the samereference characters so that, as a general rule, they will only bedescribed once.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

A first embodiment of a force measurement system is seen generally at100 in FIGS. 1-4. In the first illustrative embodiment, the forcemeasurement system 100 generally comprises a force measurement assembly10 in the form of an instrumented treadmill that is operatively coupledto a data acquisition/data processing device 60 (i.e., a dataacquisition and processing device or computing device that is capable ofcollecting, storing, and processing data), which in turn, is operativelycoupled to a subject visual display device 30 (see FIG. 9). Theinstrumented treadmill 10 is configured to receive a subject thereon. Asbest illustrated in FIG. 1, the instrumented treadmill 10 is attached tothe top of a base subassembly 20. The instrumented treadmill 10 has aplurality of top surfaces (i.e., left and right rotating belts 12, 14)that are each configured to receive a portion of a body of a subject(e.g., the left belt 12 of the instrumented treadmill 10 is configuredto receive a left leg of a subject, whereas the right belt 14 of theinstrumented treadmill 10 is configured to receive a right leg of thesubject).

In one or more embodiments, a subject walks or runs in an uprightposition atop the treadmill 10 with the feet of the subject contactingthe respective top surfaces 16, 18 of the treadmill belts 12, 14. Thebelts 12, 14 of the treadmill 10 are rotated by independent electricactuator assemblies with speed adjustment mechanisms. In the illustratedembodiment, each electric actuator assembly and associated speedadjustment mechanism comprises an electric motor with a variable speedcontrol device operatively coupled thereto. Each electric actuatorassembly and associated speed adjustment mechanism is capable ofrotating its respective treadmill belt 12, 14 at a plurality ofdifferent speeds. The speed adjustment mechanisms adjust the speed atwhich each of their respective treadmill belts 12, 14 are rotated. Thespeed adjustment mechanisms of the instrumented treadmill 10 areoperatively coupled to a programmable logic controller (PLC) 58 (seeFIG. 9). The programmable logic controller 58 of the instrumentedtreadmill 10 is operatively connected to the data acquisition/dataprocessing device 60 by an electrical cable. While they are not readilyvisible in the perspective view of FIG. 1 due to their location, theinstrumented treadmill 10 includes a plurality of force transducers(e.g., four (4) pylon-type force transducers 56—see e.g., FIG. 6)disposed below each rotating belt 12, 14 of the treadmill 10 so that theloads being applied to the top surfaces of the belts 12, 14 can bemeasured. Advantageously, the separated belts 12, 14 of the instrumentedtreadmill 10 enable the forces and/or moments applied by the left andright legs of the subject to be independently determined. The pylon-typeforce transducers 56 of the instrumented treadmill 10 are alsooperatively coupled to the treadmill programmable logic controller 58 byan electrical cable. In turn, the treadmill programmable logiccontroller 58 is operatively coupled to the data acquisition/dataprocessing device 60 so that the force and moment output data of thepylon-type force transducers 56 is capable of being analyzed andprocessed by the data acquisition/data processing device 60.

As mentioned above, each of the treadmill belts 12, 14 is supported atopfour (4) pylon-type force transducers 56 (or pylon-type load cells) thatare disposed underneath, and near each of the four corners (4) of theleft rotating belt 12 of the treadmill 10 and each of the four corners(4) of the right rotating belt 14 (see e.g., FIG. 6). Each of the eight(8) pylon-type force transducers 56 has a plurality of strain gagesadhered to the outer periphery of a cylindrically-shaped forcetransducer sensing element for detecting the mechanical strain of theforce transducer sensing element imparted thereon by the force(s)applied to the belt surfaces 16, 18 of the instrumented treadmill 10. Inthe first embodiment, each of the four (4) sets of pylon-type forcetransducers 56 are mounted atop the base subassembly 20. As best shownin the perspective view of FIG. 1, the base subassembly 20 comprises anupper body portion 21 and a lower base plate 23 disposed underneath theupper body portion 21. The instrumented treadmill 10 is also providedwith a stair 22 connected thereto so as to facilitate access to thetreadmill 10 by the subject. In the illustrative embodiment, the upperbody portion 21 of the base subassembly 20 is provided with an aluminumhoneycomb core disposed therein so as to enable the base subassembly 20to be very stiff without adding excessive weight.

In an alternative embodiment, rather than using four (4) pylon-typeforce transducers 56 on each treadmill belt assembly 12, 14, forcetransducers in the form of transducer beams could be provided under eachtreadmill belt assembly 12, 14. In this alternative embodiment, the lefttreadmill belt assembly 12 could comprise two transducer beams that aredisposed underneath, and on generally opposite sides of the treadmillbelt assembly 12. Similarly, in this embodiment, the right treadmillbelt assembly 14 could comprise two transducer beams that are disposedunderneath, and on generally opposite sides of the right treadmill beltassembly 14. Similar to the pylon-type force transducers 56, the forcetransducer beams could have a plurality of strain gages attached to oneor more surfaces thereof for sensing the mechanical strain imparted onthe beam by the force(s) applied to the surfaces 16, 18 of theinstrumented treadmill 10.

Rather, than using four (4) force transducer pylons under each treadmillbelt assembly 12, 14, or two spaced-apart force transducer beams undereach treadmill belt assembly 12, 14, it is to be understood that theinstrumented treadmill 10 can also utilize the force transducertechnology described in U.S. Pat. No. 8,544,347, the entire disclosureof which is incorporated herein by reference.

In the illustrated embodiment, the electrical cable mentioned above isused for the transmission of data between the instrumented treadmill 10and the data acquisition/data processing device 60. A separate powercable is used to provide power to the instrumented treadmill 10 (e.g., apower cable connected directly to the electrical power system of thebuilding in which the treadmill 10 is disposed). While a hardwired dataconnection is provided between the instrumented treadmill 10 and thedata acquisition/data processing device 60 in the illustrativeembodiment, it is to be understood that the instrumented treadmill 10can be operatively coupled to the data acquisition/data processingdevice 60 using other signal transmission means, such as a wireless datatransmission system.

Now, turning to FIG. 9, it can be seen that the illustrated dataacquisition/data processing device 60 (i.e., the operator computingdevice) of the force measurement system 100 includes a microprocessor 60a for processing data, memory 60 b (e.g., random access memory or RAM)for storing data during the processing thereof, and data storagedevice(s) 60 c, such as one or more hard drives, compact disk drives,floppy disk drives, flash drives, or any combination thereof. As shownin FIG. 9, the programmable logic controller (PLC) 58 of theinstrumented treadmill 10, and the subject visual display device 30 areoperatively coupled to the data acquisition/data processing device 60such that data is capable of being transferred between these devices 30,58, and 60. Also, as illustrated in FIG. 9, a plurality of data inputdevices 64, 66, such as a keyboard and mouse, are diagrammatically shownin FIG. 9 as being operatively coupled to the data acquisition/dataprocessing device 60 so that a user is able to enter data into the dataacquisition/data processing device 60. Also, as depicted in FIG. 9, anoperator visual display device 62 may also be operatively coupled to thedata acquisition/data processing device 60 so that an operator (e.g.,clinician) of the force measurement system 100 has a more convenientdedicated display, and thus, is not required to use the subject visualdisplay device 30. In some embodiments, the data acquisition/dataprocessing device 60 can be in the form of a desktop computer, while inother embodiments, the data acquisition/data processing device 60 can beembodied as a laptop computer.

Advantageously, the programmable logic controller 58 (see e.g., FIG. 9,which is a type of data processing device) provides real-time control ofthe treadmill actuators (i.e., motors) that control the rotation of theleft and right treadmill belts 12, 14. The real-time control provided bythe programmable logic controller 58 ensures that the softwareregulating the control of the left and right treadmill belts 12, 14operates at the design clock rate, thereby providing fail-safe operationfor subject safety. In one embodiment, the programmable logic controller58 comprises both the treadmill control software and the input/outputmanagement software, which controls the functionality of theinput/output (I/O) module of the programmable logic controller 58. Inone embodiment, the programmable logic controller 58 utilizes EtherCATprotocol for enhanced speed capabilities and real-time control.

In one or more embodiments, the input/output (I/O) module of theprogrammable logic controller 58 allows various accessories to be addedto the force measurement system 100. For example, an eye movementtracking system, such as that described by U.S. Pat. Nos. 6,113,237 and6,152,564 could be operatively connected to the input/output (I/O)module of the programmable logic controller 58. As another example, ahead movement tracking system, which is instrumented with one or moreaccelerometers, could be operatively connected to the input/output (I/O)module.

In one or more embodiments, an emergency stop switch may be operativelycoupled to the programmable logic controller 58 in order toquasi-instantaneously stop the rotation of the treadmill belts 12, 14.As such, the emergency stop switch is a safety mechanism that protects asubject disposed on the instrumented treadmill 10 from potential injury.In an exemplary embodiment, the emergency stop switch may be in the formof a red pushbutton that can be easily pressed by a user of the forcemeasurement system 100 in order to stop the rotation of the treadmillbelts 12, 14.

Now, the acquisition and processing of the load data carried out by theforce measurement system will be described. Initially, a load is appliedto the instrumented treadmill 10 by a subject disposed thereon. The loadis transmitted from the treadmill belt assemblies 12, 14 to itsrespective set of pylon-type force transducers 56 (or force transducerbeams). As described above, in the illustrated embodiment, eachtreadmill belt assembly 12, 14 comprises four (4) pylon-type forcetransducers 56 disposed thereunder. Preferably, these pylon-type forcetransducers 56 are disposed near respective corners of each treadmillbelt assembly 12, 14. In a preferred embodiment, each of the pylon-typeforce transducers 56 includes a plurality of strain gages wired in oneor more Wheatstone bridge configurations, wherein the electricalresistance of each strain gage is altered when the associated portion ofthe associated pylon-type force transducer undergoes deformationresulting from the load (i.e., forces and/or moments) acting on thetreadmill belt assemblies 12, 14. For each plurality of strain gagesdisposed on the pylon-type force transducers 56, the change in theelectrical resistance of the strain gages brings about a consequentialchange in the output voltage of the Wheatstone bridge (i.e., a quantityrepresentative of the load being applied to the measurement surface).Thus, in one embodiment, the four (4) pylon-type force transducers 56disposed under each treadmill belt assembly 12, 14 output a total ofthirty-two (32) raw output voltages (signals) in either analog ordigital form. In some embodiments, if the output voltages (signals) arein analog form, the thirty-two (32) raw output voltages (signals) fromeach treadmill belt assembly 12, 14 are then transmitted to apreamplifier board for preconditioning. The preamplifier board is usedto increase the magnitudes of the transducer analog voltages. Afterwhich, in one or more embodiments, the analog output signalsS_(APO1)-S_(APO32) are transmitted from the analog preamplifier to thetreadmill programmable logic controller (PLC) 58. In the treadmillprogrammable logic controller 58, the analog output signalsS_(APO1)-S_(APO32) are converted into forces, moments, centers ofpressure (COP), subject center of gravity (COG), and/or sway angle forthe subject. Then, the forces, moments, centers of pressure (COP),subject center of gravity (COG), and/or sway angle for the subjectcomputed by the programmable logic controller 58 are transmitted to thedata acquisition/data processing device 60 (operator computing device60) so that they can be utilized for analyzing the movement of thesubject and/or for reports displayed to an operator or clinician. Also,in yet another embodiment, the preamplifier board additionally could beused to convert the analog voltage signals into digital voltage signals(i.e., the preamplifier board could be provided with ananalog-to-digital converter). In this embodiment, digital voltagesignals would be transmitted to the treadmill programmable logiccontroller 58 rather than analog voltage signals.

In one or more embodiments, when the programmable logic controller 58receives the voltage signals S_(ACO1)-S_(ACO32), it initially transformsthe signals into output forces and/or moments by multiplying the voltagesignals S_(ACO1)-S_(ACO32) by a calibration matrix. After which, theforce and moment components (i.e., F_(Lx), F_(Ly), F_(Lz), M_(Ly),M_(Lz)) exerted on the left belt surface 16 of the left treadmill beltassembly 12 by the left foot of the subject, the force and momentcomponents (i.e., F_(Rx), F_(Ry), F_(Rz), M_(Rx), M_(Ry), M_(Rz))exerted on the right belt surface 18 of the right treadmill beltassembly 14 by the right foot of the subject, and the center of pressure(x_(P) _(L) , y_(P) _(L) ; X_(P) _(R) , y_(P) _(R) ) for each foot ofthe subject (i.e., the x and y coordinates of the point of applicationof the force applied to the measurement surface by each foot) aredetermined by the programmable logic controller 58, and then transmittedto the data acquisition/data processing device 60.

Now, with reference to FIGS. 1-4, the subject visual display device 30of the force measurement system 100 will be described in more detail. Inthe illustrated embodiment, the subject visual display device 30generally comprises a projector 40 with a fisheye lens 44, and a concaveprojection screen 31 with a cylindrical middle portion and spherical topand bottom portions. In other words, in the illustrative embodiment, theprojection screen 31 of the force measurement system 100 is not entirelyspherically-shaped or dome-shaped. Advantageously, because the concaveprojection screen 31 is cylindrical in the middle with spherical partson the top and bottom, a focal line is created for the subject standingon the instrumented treadmill 10, rather than a single focal point whichwould be created if the screen 31 were entirely spherical in shape.Thus, advantageously, individuals of different heights may beaccommodated within the confines of the concave projection screen 31without adversely affecting the focal region during the immersion (i.e.,the height of a subject does not materially affect the immersive effectof the concave projection screen 31).

Turning again to the illustrative embodiment of FIGS. 1-4, the projector40 with the fisheye-type lens 44 projects a light beam through asemi-circular cutout 34 in the top of the concave projection screen 31.In FIG. 1, it can be seen that the fisheye lens 44 is connected to thebody of the projector 40 by an elbow fitting 42. Also, as best shown inFIGS. 1 and 2, the concave projection screen 31 may be provided with aperipheral flange 33 therearound. Advantageously, the concave projectionscreen 31 is a continuous curved surface that does not contain any linesor points resulting from the intersection of adjoining planar or curvedsurfaces (i.e., all section seams in the screen 31 may be filled so asto form a continuous curved surface facing the subject). Thus, theprojection screen 31 is capable of creating a completely immersivevisual environment for a subject being tested on the instrumentedtreadmill 10 because the subject is unable to focus on any particularreference point or line on the screen 31. As such, the subject becomescompletely immersed in the virtual reality scene(s) being projected onthe concave projection screen 31, and thus, his or her visual perceptioncan be effectively altered during a test being performed using the forcemeasurement system 100 (e.g., a balance test). In order to permit asubject to be substantially circumscribed by the generally hemisphericalprojection screen 31 on three sides, the bottom of the screen 31 isprovided with a semi-circular cutout 32 in the illustrative embodiment.While the concave projection screen 31 thoroughly immerses the subjectin the virtual reality scene(s), it advantageously does not totallyenclose the subject. Totally enclosing the subject could cause him orher to become extremely claustrophobic. Also, the clinician would beunable to observe the subject or patient in a totally enclosedenvironment. As such, the illustrated embodiment of the forcemeasurement system 100 does not utilize a totally enclosed environment,such as a closed, rotating shell, etc. Also, the subject visual displaydevice 30 is not attached to the subject, and it is spaced apart fromthe instrumented treadmill 10.

In one embodiment of the invention, the generally hemisphericalprojection screen 31 is formed from a suitable material (e.g., anacrylic, fiberglass, fabric, aluminum, etc.) having a matte gray color.A matte gray color is preferable to a white color because it minimizesthe unwanted reflections that can result from the use of a projectionscreen having a concave shape. Also, in an exemplary embodiment, theprojection screen 31 has a diameter (i.e., width W_(S)) of approximately180 inches and a depth D_(S) of approximately 90 inches. Although, thoseof ordinary skill in the art will readily appreciate that other suitabledimensions may be utilized for the projection screen 31, provided thatthe selected dimensions for the screen 31 are capable of creating animmersive environment for a subject disposed on the instrumentedtreadmill 10 (i.e., the screen 31 of the subject visual display device30 engages enough of the subject's peripheral vision such that thesubject becomes, and remains immersed in the virtual reality scenario).In one or more embodiments, the projection screen 31 fully encompassesthe peripheral vision of the subject (e.g., by the coronal plane CP ofthe subject being disposed inwardly from the flange 33 within theconfines of the screen 31). In other words, the output screen 31 of theat least one visual display 30 at least partially circumscribes threesides of a subject. The overhanging top portion of the projection screen31 creates an efficient manner in which to fully immerse the subject. Ifthe projection screen 31 were not formed with the overhanging topportion, the height of the projection screen 31 would have to be greatlyincreased in order to create the same full immersive effect. As such,the use of the concave projection screen 31 with the spherical,overhanging top portion allows the screen 31 to be much shorter, whilestill achieving the desired effect of the total immersion of thesubject.

With particular reference to FIGS. 1, 2, and 4, it can be seen that, inthe illustrated embodiment, the concave projection screen 31 of the atleast one visual display 30 is formed from a plurality of sections 31a-31 h. Specifically, in the illustrative embodiment, referringinitially to the front view of FIG. 2, it can be seen that the concaveprojection screen 31 comprises a first top left end section 31 a, asecond top left middle section 31 b, a third top right middle section 31c, a fourth top right end section 31 d, a fifth bottom left end section31 e, a sixth bottom left middle section 31 f, a seventh bottom rightmiddle section 31 g, and an eighth bottom right end section 31 h. Asshown in FIG. 1, each of these screen sections 31 a-31 h comprises oneor more connector flanges 46 that are used to connect the screensections 31 a-31 h to one another (e.g., the screen sections 31 a-31 hare bolted to one another). Advantageously, forming the concaveprojection screen 31 from a plurality of separate, interconnectablesections 31 a-31 h allows the concave projection screen 31 to be moreeasily installed inside the room of a building because the screen 31 canbe transported in sections 31 a-31 h, and then subsequently installedonce it is inside the room (i.e., the sections 31 a-31 h may beconnected together once inside the room). As such, the sectionalconstruction of the concave projection screen 31 obviates the need for alarge opening (e.g., a door opening) into the room in which the screen31 is being installed.

In a preferred embodiment, the data acquisition/data processing device60 is configured to convert a two-dimensional (2-D) image, which isconfigured for display on a conventional two-dimensional screen, into athree-dimensional (3-D) image that is capable of being displayed on thehemispherical output screen 31 without excessive distortion. That is,the data acquisition/data processing device 60 executes a softwareprogram that utilizes a projection mapping algorithm to “warp” a flat2-D rendered projection screen image into a distorted 3-D projectionimage that approximately matches the curvature of the final projectionsurface (i.e., the curvature of the hemispherical output screen 31),which takes into account the distortion of the lens 44 of the projector40. In particular, the projection mapping algorithm utilizes a pluralityof virtual cameras and projection surfaces (which are modeled based uponthe actual projection surfaces) in order to transform thetwo-dimensional (2-D) images into the requisite three-dimensional (3-D)images. Thus, the projector lens 44 information and the concaveprojection screen 31 dimensional data are entered as inputs into theprojection mapping algorithm software. When a human subject is properlypositioned in the confines of the hemispherical output screen 31, he orshe will see a representation of the virtual reality scene wrappingaround them instead of only seeing a small viewing window in front ofhim or her. Advantageously, using a software package comprising aprojection mapping algorithm enables the system 100 to use previouslycreated 3-D modeled virtual worlds and objects without directlymodifying them. Rather, the projection mapping algorithm employed by thesoftware package merely changes the manner in which these 3-D modeledvirtual worlds and objects are projected into the subject's viewingarea.

As described above, with reference to FIG. 1, it can be seen that thefisheye lens 44 of the projector 40 is connected to the body of theprojector 40 by an elbow fitting 42. In other words, the fisheye lens 44is disposed at a non-zero, angled orientation relative to a body of theprojector 40. In the illustrated embodiment, the non-zero, angledorientation at which the fisheye lens 44 is disposed relative to thebody of the projector 40 is approximately 90 degrees. The elbow fitting42 comprises a one-way mirror disposed therein for changing thedirection of the light beam emanating from the projector 40. Asillustrated in FIG. 1, the fisheye lens 44 is disposed at approximatelythe apex of the concave projection screen 31, and it extends downthrough the cutout 34 at the top of the screen 31.

Those of ordinary skill in the art will also appreciate that the subjectvisual display device 31 may utilize other suitable projection means.For example, rather using an overhead-type projector 40 as illustratedin FIGS. 1-4, a direct or rear projection system can be utilized forprojecting the image onto the screen 31, provided that the directprojection system does not interfere with the subject's visibility ofthe target image. In another alternative embodiment, two projectors,each having a respective fisheye-type lens, are used to project an imageonto the screen 31. In this alternative embodiment, the two projectorswith respective fisheye-type lens project intersecting light beamsthrough the cutout 34 in the top of the generally hemisphericalprojection screen 31. Advantageously, the use of two projectors withrespective fisheye-type lens, rather than just a single projector 40with a fisheye lens 44, has the added benefit of removing shadows thatare cast on the output screen 31 by the subject disposed on theinstrumented treadmill 10.

Referring collectively to FIGS. 1-4, it can be seen that, in theillustrative embodiment, the concave projection screen 31 may besupported from a floor surface using a screen support structure formedusing a plurality of truss members 24, 26, 28. As shown in FIGS. 1, 2,and 4, the screen support structure 24, 26, 28 is used to elevate theprojection screen 31 a predetermined distance above the floor of a room.With continued reference to FIGS. 1, 2, and 4, it can be seen that theillustrated screen support structure comprises a plurality of generallyvertical truss members 24 (i.e., three (3) generally vertical trussmembers 24) that support a plurality of generally horizontal trussmembers 26, 28 (i.e., two (2) generally horizontal truss members 26,28), which are disposed at the top of the projection screen 31. As bestshown in FIGS. 1 and 3 of the illustrated embodiment, the plurality ofgenerally horizontal truss members 26, 28 include a first linear trussmember 26 disposed in the front of the projection screen 31, and asecond semi-circular truss member 28 disposed around the curved backside of the projection screen 31. In particular, the two (2) frontvertical truss members 24 are securely attached to the peripheral flange33 of the concave projection screen 31 (e.g., by using a plurality offasteners and brackets on each side of the flange 33). Because thescreen support structure 24, 26, 28 is mostly attached to the upperportion (e.g., upper half) of the screen 31, the screen 31 is generallysupported above its center-of-gravity, which advantageously results in ascreen mounting arrangement with high structural stability. As shown inFIGS. 1 and 2, one of the plurality of lower leg members 38 are disposedon each of the opposed lateral sides of the screen 31. Also, each of thelower leg members 38 may be provided with a height-adjustable foot foradjusting the height of the screen 31 relative to the floor. Also, asshown in FIGS. 1 and 3, the projector 40 is supported above the screen31 by a pair of spaced-apart projector support rails 36, each of whichis secured directly to the first linear truss member 26 and the secondsemi-circular truss member 28 of the screen support structure 24, 26,28, and not directly to the screen 31, so as to minimize thetransmission of vibrations from the projector 40 to the hemisphericalprojection screen 31. Advantageously, the mounting arrangement of theprojector 40 on the spaced-apart projector support rails 36 affordsadjustability of the projector 40 in a front-to-back direction. It ishighly desirable for the hemispherical projection screen 31 to bemaintained in a stationary position essentially free from externalvibrations so that the subject is completely immersed in the virtualenvironment being created within the hemispherical projection screen 31.Advantageously, the structural rigidity afforded by the screen supportstructure 24, 26, 28 of FIGS. 1-4 virtually eliminates the transmissionof vibrations to the projection screen 31, including those vibrationsemanating from the building itself in which the force measurement system100 is located. In particular, the screen support structure 24, 26, 28is designed to minimize any low frequency vibrations that aretransmitted to the screen 31.

In the illustrative embodiment, as best shown in the top view of FIG. 3,the top surfaces 16, 18 of the treadmill belts 12, 14 are horizontallyspaced apart from the screen support structure 24, 26, 28. In otherwords, there is a gap horizontally separating the instrumented treadmill10 from the hemispherical projection screen 31 and its associated screensupport structure 24, 26, 28.

As shown in the illustrative embodiment of FIGS. 1-4, the forcemeasurement system 100 may be additionally provided with a motioncapture system comprising a plurality of cameras 50. Initially,referring to FIG. 1, it can be seen that a plurality of cameras 50 aredisposed around the instrumented treadmill 10 so that the cameras 50 atleast partially surround subject disposed on the treadmill 10. In theillustrative embodiment, the cameras 50 are used to track positions of aplurality of markers disposed on a subject as the subject moves his orher torso and limbs in 3-dimensional space. The markers on the subjectare used to record the position of the torso and limbs of the subject in3-dimensional space.

In the illustrative embodiment, with reference to FIGS. 1 and 3, it canbe seen that a first plurality of cameras 50 are circumferentiallyspaced apart around the top cutout 34 in the concave projection screen31 (i.e., the first plurality of cameras 50 are structurally attached ina load bearing manner around the top cutout 34 of the concave projectionscreen 31). For example, as best shown in the top view of FIG. 3, thecameras 50 may be generally equally spaced apart about the circumferenceof the top screen cutout 34. While five (5) cameras 50 are depictedaround the circumference of the top screen cutout 34 in the illustrativeembodiment, one of ordinary skill in the art will appreciate that moreor less cameras may be utilized, provided that the motion of the subjectis capable of being captured from substantially all angles. Turning toFIGS. 1 and 2, it can be seen that a second plurality of cameras 50 arespaced apart in front of the instrumented treadmill 10 (i.e., on theopen front side of the projection screen 31). In particular, as shown inthe illustrative embodiment of FIG. 2, one (1) camera 50 is disposed oneach of the generally vertical truss members 24 near the approximatemiddle of the truss member 24 (i.e., each camera 50 is structurallyattached to a respective vertical truss members 24 in a load bearingmanner approximately mid-height on the truss member 24). Two (2)additional cameras 50 are attached to the camera mounting structure 48that extends outwardly from the truss members 24, 26 (i.e., the twoadditional cameras 50 are structurally attached to the camera mountingstructure 48 in a load bearing manner). With combined reference to FIGS.1 and 2, it can be seen that the camera mounting structure 48 isattached to each of the vertical truss members 24 and the generallylinear truss member 26. The camera mounting structure 48 enables the two(2) additional front cameras 50 to be spaced significantly in front ofthe cameras 50 that are mounted to the respective vertical truss members24 so that the movements of the subject may be better captured by themotion capture system. While a total of nine (9) cameras 50 are depictedin the illustrative embodiment of FIGS. 1-4, one of ordinary skill inthe art will appreciate that more or less cameras can be utilized,provided that the motion of the subject is capable of being capturedfrom substantially all angles.

In the illustrative embodiment, the cameras 50 depicted in FIGS. 1-4 maybe in the form of infrared-type (IR) or near infrared-type (NIR) camerashaving an angular field of view range between approximately 40 degreesand approximately 80 degrees (or between 40 degrees and 80 degrees).More particularly, in one or more embodiments, the angular field of viewrange of the cameras 50 may be between approximately 50 degrees andapproximately 70 degrees (or between 50 degrees and 70 degrees). Also,in one or more exemplary embodiments, the cameras 50 depicted in FIGS.1-4 may have a resolution of approximately 1.0 Megapixels, a maximumframe rate of approximately 250 feet per second (fps), and a 4millimeter to 12 millimeter (4-12 mm) zoom lens. The cameras 50 arepositioned in the force measurement system 100 of FIGS. 1-4 so that eachmarker disposed on a subject standing on the instrumented treadmill 10is captured by at least two (2) of the cameras 50, and preferably, three(3) of the cameras 50.

In one embodiment of the invention, a subject has a plurality of singlereflective markers applied to anatomical landmarks (e.g., the iliacspines of the pelvis, the malleoli of the ankle, and the condyles of theknee), and/or clusters of markers applied to the middle of bodysegments. As the subject executes particular movements on theinstrumented treadmill 10, the data acquisition/data processing device60 is specially programmed to calculate the trajectory of eachreflective marker in three (3) dimensions using the position of themarker captured by the cameras 50. Then, once the positional data isobtained using the motion capture system of FIGS. 1-4, inversekinematics may be employed in order to further determine the jointangles of the subject. That is, the motion capture system of FIGS. 1-4generates motion capture data that is representative of the capturedmotion of the body portions of the subject, and the dataacquisition/data processing device 60 is specially programmed todetermine the position of the body of the subject (i.e., limbs, torso,head, etc.) and the joint angles of the subject from the motion capturedata generated by the motion capture system.

While the motion capture system of FIGS. 1-4 described above employs aplurality of reflective markers, it is to be understood that theinvention is not so limited. Rather, in another embodiment of theinvention, a markerless motion detection/motion capture system isutilized. The markerless motion capture system uses a plurality of highspeed video cameras to record the motion of a subject without requiringany markers to be placed on the subject. Also, while the illustrativeembodiment utilizes a plurality of infrared-type (IR) or nearinfrared-type (NIR) cameras 50, it is to be understood that anon-infrared, optical-based motion detection/motion capture system mayalternatively be used. For example, in one alternative embodiment, theoptical motion capture system utilizes visible light, rather thaninfrared light. In addition, an alternative motion capture system mayutilize an infrared (IR) emitter to project a plurality of dots ontoobjects in a particular space as part of a markerless motion capturesystem. For example, in these one or more alternative embodiments, themarkerless motion capture system may comprise a motion capture devicewith one or more cameras, one or more infrared (IR) depth sensors, andone or more microphones, which may be used to provide full-bodythree-dimensional (3D) motion capture, facial recognition, and voicerecognition capabilities. It is also to be understood that, rather thanusing an optical motion detection/capture system, a suitable magnetic orelectro-mechanical motion detection/capture system may also be employedto determine the position and joint angles of the subject on theinstrumented treadmill 10.

A second embodiment of the force measurement system is seen generally at200 in FIGS. 5 and 6. With reference to these figures, it can be seenthat the force measurement system 200 is similar in most respects to theforce measurement system 100 of the first embodiment described above.However, unlike the aforedescribed force measurement system 100, theinstrumented treadmill 10′ is mounted to the top of a motion basesubassembly 20′, rather than to the static base subassembly 20 of thefirst embodiment. As shown in FIGS. 5 and 6, the motion base subassembly20′ comprises a motion base 52 that is capable of displacing theinstrumented treadmill 10′ in a plurality of different directions. Inthe illustrated embodiment, the motion base 52 is in the form of a two(2) degree-of-freedom motion base. However, in one or more otherembodiments, the motion base 52 may be a six (6) degree-of-freedommotion base that is capable of both translating and rotating theinstrumented treadmill 10, 10′ in 3-dimensional space (i.e., translatingand rotating the instrumented treadmill 10, 10′ in all three (3)coordinate directions). Referring again to the second embodiment ofFIGS. 5 and 6, it can be seen that the instrumented treadmill 10′ isdisposed in the middle of a treadmill platform 54. The treadmillplatform 54, which is disposed on both sides of the instrumentedtreadmill 10′, makes it easier for the subject to get on and off of theinstrumented treadmill 10′ during testing.

With reference to the block diagram of FIG. 10, the hardware andsoftware architecture of the illustrative embodiments of the forcemeasurement systems 100, 200 will be described in detail. As shown inFIG. 10, the force measurement systems 100, 200 generally include ahardware layer 70, a system implementation layer 72, a systemintegration software layer 74, a virtual reality dynamic-link library(DLL) software layer 76, and a user-developed virtual reality interfacesoftware layer 78 (or user-developed application software layer 78).Each of these hardware and software layers 70, 72, 74, 76, 78 will bedescribed in detail hereinafter, along with the data transfer paths82-98, 102, and 104 between these layers 70, 72, 74, 76, 78. In theillustrative embodiment, hardwired connections may form the datatransfer paths 82-98, 102, and 104 between the constituent components ofthe force measurement systems 100, 200. Alternatively, data may betransferred wirelessly between the components of the force measurementsystems 100, 200 depicted in FIG. 10.

Throughout the present disclosure, when a reference is made to a dataacquisition/data processing device 60 or computing device that is“configured to”, “arranged to” and/or “configured and arranged to”perform a specific function (e.g., a data acquisition/data processingdevice 60 configured and arranged to perform a specific function), it isto be understood that, in one or more embodiments of the invention, thismeans that the data acquisition/data processing device or computingdevice is specially programmed to carry out the particular function(e.g., the data acquisition/data processing device 60 being speciallyprogrammed to perform a specific function).

Initially, referring to FIG. 10, it can be seen that the hardware layer70 of the force measurement systems 100, 200 includes the instrumentedtreadmill 10, 10′, the spherical screen 31 and projector 40 of thevisual display device, the cameras 50 of the motion capture system, themotion base 52 on which the instrumented treadmill 10′ of the secondembodiment is mounted, and any auxiliary input/output devices 68. Forexample, as mentioned above, the force measurement systems 100, 200 mayinclude auxiliary input/output devices 68, such as an eye movementtracking system (e.g., as described by U.S. Pat. Nos. 6,113,237 and6,152,564, which are incorporated by reference in their entiretiesherein). In addition, as also mentioned above, the auxiliaryinput/output devices 68 of the systems 100, 200 may include a headmovement tracking system comprising one or more accelerometers formeasuring the head position and/or velocity of the subject. Also, theauxiliary input/output devices 68 of the systems 100, 200 may furtherinclude one or more devices to measure the speed of the treadmill beltsand one or more inertial measurement units (IMUs) for measuring themovement of the subject disposed on the instrumented treadmill 10, 10′.The auxiliary input/output devices 68 of the systems 100, 200 may alsoinclude a galvanic stimulator that sends an electrical signal to aportion of the body of the subject, one or more treadmill belttachometers that measure the treadmill belt rotational speed directly,and/or a hand trigger connected to the analog-to-digital (A/D) board.

Next, with reference again to FIG. 10, the system implementation layer72, the system integration software layer 74, the virtual realitydynamic-link library (DLL) software layer 76, and the user-developedvirtual reality interface software layer 78 of the force measurementsystems 100, 200 will be described. As shown in FIG. 10, the systemimplementation layer 72 includes the programmable logic controller (PLC)58 and motion capture (MoCap) software 80. The functionality of theprogrammable logic controller 58 was described above. In theillustrative embodiment, which employs a marker-based motion capturesystem, the motion capture (MoCap) software 80 is used to analyze thereflective markers attached to the subject. The motion capture (MoCap)software 80 may also utilize analog/digital data from the instrumentedtreadmill 10, 10′ to calculate joint kinematics and kinetics andidentify gait events, such as heel strike. The system integrationsoftware layer 74 comprises the software 75 that synchronizes data fromthe instrumented treadmill 10, 10′ and the camera data processed by themotion capture software 80. The system integration software 75 has thecapability to connect any auxiliary input/output devices 68, such asfoot switches, EMG devices, galvanic stimulators, inertial measurementunits (IMUs), and head/eye trackers through an analog-to-digital (A/D)board. All of this data is synchronized in real-time to process anddisplay information, such as joint kinematics and kinetics, groundreaction forces, spatiotemporal parameters of gait, muscle activation,and rigid body positions. Gait events, such as heel strike and toe-offcan be identified. The software also provides real-time biofeedback interms of visual and/or auditory feedback. Visual feedback is throughcommunication with the user-developed virtual reality interface softwarelayer 78 (or the user-developed application software 78). The auditoryfeedback comprises one or more speakers provided as part of the forcemeasurement system 100, 200. For example, as shown in the illustrativeembodiment of FIG. 1, speakers 25 may be provided on the vertical trussmembers 24. The speakers 25 are operatively coupled to the dataacquisition/data processing device 60 so as to be capable of providingauditory feedback described hereinafter. In the illustrative embodiment,a target may be set up for one gait parameter, such as knee flexionangle, and once that target is reached, an auditory or visual feedbackis given to the subject. The virtual reality dynamic-link library (DLL)software layer 76 comprises a plurality of executable files that allowsthe various programs of the force measurement systems 100, 200 to sharecode and other resources necessary to perform the particular tasks ofthe systems 100, 200 (e.g., virtual reality tasks, etc.). In theillustrative embodiment, the virtual reality dynamic-link library (DLL)software layer 76 is visible to the system user of the force measurementsystem 100, 200. The system architecture layers below the virtualreality DLL software layer 76 (e.g., system implementation layer 72 andthe system integration layer 74) are hidden from the system user so asto protect the system data stored in these layers 72, 74 from beinginadvertently modified by the system user. In the illustrativeembodiment, the virtual reality DLL software layer 76 is in the form ofan executable/graphical user interface (GUI)/example software code thatlists the variables that the user is able to use to design or modifyusing the visual interface. The virtual reality DLL software layer 76also lists the variable names that can be accessed from the systemintegration software 75, which includes data from the instrumentedtreadmill 10, 10′ and the motion capture (MoCap) software 80. Theuser-developed virtual reality interface software layer 78 (oruser-developed application software layer 78) is responsible for thevisual stimulus feedback. The user-developed application software 78allows the system user to program the visual scenes that providefeedback to the subject (e.g., the closed loop biofeedback describedhereinafter). These visual scenes may be standalone, open loop feedbackor closed loop feedback. An example of a standalone visual scene is justprojecting an animation with no communication between the systemintegration software/treadmill/cameras and the visual scene itself. Withopen loop feedback, the data from the system integration software 75 ispassed to the visual scene and the visual stimulus is synchronized witheither the instrumented treadmill 10, 10′ or the cameras 50. In theillustrative embodiment, the treadmill belt speed and the speed scalefactor is sent to the user-developed application software 78 which, inturn, uses these parameters to set the speed of the optic flow. Thus,the optic flow is able to be synchronized with the treadmill belt speed.As another example, a pelvic marker position may be sent to theuser-developed application software 78 so that the optic flow may besynchronized with the pelvic marker instead. The ground reaction forcesand the center-of-pressure (COP) determined using the instrumentedtreadmill 10, 10′ are also sent to the user-developed applicationsoftware 78 so that the visual scene is capable of being changed basedon the ground reaction forces and/or the center-of-pressure of thesubject. In the illustrative embodiment, different levels of difficultyare capable of being set up in the visual scene based on the subjectperformance. The subject performance may be quantified based on thetreadmill or camera data. For example, the ground reaction force duringheel strike or the position of some joint. The closed loop feedbackfunctionality of the force measurement systems 100, 200 will bedescribed in detail hereinafter. As one example of closed loop feedbackcarried out by the system 100, 200, the belt speed of the instrumentedtreadmill 10, 10′ changes in accordance with the visual scene on thespherical screen 31 of the visual display device 30.

In one or more embodiments, the force measurement systems 100, 200 mayeach comprise two (2) data acquisition/data processing devices (i.e.,two (2) computers) for executing the software described above. The firstcomputer has the treadmill control software, the motion capture software80, and the system integration software 75 loaded thereon. The secondcomputer has the virtual reality software 76 and the user-developedapplication software 78 loaded thereon. In one or more alternativeembodiments, the force measurement systems 100, 200 may each comprise asingle data acquisition/data processing device 60 (i.e., a singlecomputer) for executing the software described above. In these one ormore alternative embodiments, the data acquisition/data processingdevice 60 may have the treadmill control software, the motion capturesoftware 80, the system integration software 75, the virtual realitysoftware 76, and the user-developed application software 78 all loadedthereon.

In the illustrative embodiment, the force measurement systems 100, 200are capable of providing both explicit motor training and implicit motortraining for the subject. When explicit motor training is provided, thescene displayed on the spherical screen 31 of the visual display device30 merely graphically depicts the movement of the subject so as toprovide feedback to the subject. For example, in the case of explicitfeedback, the height of the subject's foot from the surface level and/orthe joint kinematics of the subject may be displayed on the sphericalscreen 31 of the visual display device 30. Although, when implicit motortraining is provided, the subject is in control of the feedback that isprovided on the spherical screen 31 of the visual display device 30. Forexample, in the case of implicit feedback, when a subject is progressingdown a virtual grocery store aisle on the spherical screen 31 of thevisual display device 30 (e.g., as shown in FIGS. 11 and 12), the numberof obstacles 114 avoided by the subject, and the number of obstacles 114that the subject collides with may be recorded by the dataacquisition/data processing device 60 of the system 100, 200. The dataacquisition/data processing device 60 of the system 100, 200 may also bespecially programmed to display the recorded obstacle avoidance andobstacle collision quantities on the spherical screen 31 of the visualdisplay device 30 in order to provided implicit feedback to the subjectundergoing the training or testing on the instrumented treadmill 10,10′.

With reference to FIGS. 11-12, an immersive grocery aisle scene inaccordance with one illustrative embodiment of the invention will bedescribed. Initially, with reference to FIG. 11, it can be seen that thegrocery aisle screen image 110 comprises a grocery aisle 112 bounded bya plurality of shelves 116 disposed on each of the opposite sides of thegrocery aisle 112. A plurality of obstacles (e.g., boxes 114) isdisposed in the grocery aisle 112 so that the subject is required tomaneuver around the obstacles 114 in an effort to avoid colliding withone of the obstacles 114. The grocery aisle screen image 110′ of FIG. 12is identical to the grocery screen image 110 of FIG. 11, except that thescreen image 110′ comprises a star 118 disposed in the screen image110′. The star 118 represents the position of the subject in the screenimage 110′. In one or more alternative embodiments, the star 118 may bereplaced with an avatar or a silhouette of the subject in the screenimage 110′. In the immersive grocery aisle scenario of FIGS. 11 and 12,the data acquisition/data processing device 60 may be speciallyprogrammed to control the movement of the star 118 on the screen inaccordance with the center of pressure (COP) determined by theinstrumented treadmill 10, 10′. For example, when a subject leans to theleft on the instrumented treadmill 10, 10′, the star 118 in theimmersive grocery aisle scene is displaced to the left. Conversely, whena subject leans to the right on the instrumented treadmill 10, 10′, thestar 118 in the immersive grocery aisle scene is displaced to the right.In this manner, the subject is able to avoid colliding with theobstacles 114 in the immersive grocery aisle scene by appropriatelyshift his or her weight to the right or to the left, thereby moving thestar 118 to a side of the obstacle 114. In the immersive grocery aislescenario of FIGS. 11 and 12, when a subject collides with one of theobstacles 114 in the scene (i.e., when the star 118 representing thesubject collides with one of the obstacles 114), the dataacquisition/data processing device 60 may be specially programmed toreduce the treadmill belt speed so as to simulate a collision with thevirtual obstacle 114 (i.e., by reducing the speed set point sent to thespeed adjustment mechanisms of the treadmill belts). Then, after thesubject clears the virtual obstacle 114 (i.e., once the star 118 isshifted to a side of the obstacle 114 by the subject), the dataacquisition/data processing device 60 may be specially programmed toincrease the treadmill belt speed to its speed prior to the collisionwith the virtual obstacle 114 so that the subject may continue toprogress down the virtual grocery aisle in a normal fashion. AlthoughFIGS. 11 and 12 depict generally planar images, rather than a concaveimage projected on the spherical screen 31 of the visual display device30, it is to be understood that the immersive grocery aisle scenario,like the other scenarios described hereinafter, is configured to beimplemented on the spherical screen 31 that at least partially surroundsthe subject.

In a further embodiment, while walking through the immersive groceryaisle scene of FIGS. 11-12, the subject may be instructed to overcomeobstacles 114 by lifting his foot so as to step over the obstacles 114.In this further embodiment, a reflective marker may be attached to thefoot of the subject so that the cameras 50 of the motion capture systemdescribed above are able to detect the foot position of the subject bymeans of this reflective marker. If the foot is raised high enough bythe subject, the subject clears the obstacle 114. However, if thesubject does not raise his or her foot to the desired height so as toclear the obstacle 114, the data acquisition/data processing device 60may be programmed to generate a red line on the scene which indicatesthe additional height the foot has to reach. In one or more embodiments,the data acquisition/data processing device 60 may be programmed tocompute an error term by subtracting the actual foot height achieved bythe subject from the height of the obstacle 114 (i.e., ObstacleHeight−Foot Height From Marker=Error). In these embodiments, theacquisition/data processing device 60 determines the height of the redline in the scene by adding the error term to the actual foot heightachieved by the subject. In one or more other embodiments, the dataacquisition/data processing device 60 may be programmed to compute anaugmented error term by multiplying the aforedescribed error term by anumerical factor (e.g., 1.25, 1.5, 2.0, etc.). In these embodiments, theacquisition/data processing device 60 determines the height of the redline in the scene by adding the augmented error term to the actual footheight achieved by the subject. As such, the error term may bedifference between the desired and current foot position, or in case ofaugmented error, the error term may be multiplied by a numerical factor.

Now, referring again to FIG. 10, the data transfer paths 82-98, 102, and104 between the hardware and software layers 70, 72, 74, 76, 78 of theforce measurement systems 100, 200 will be explained. In FIG. 10, it canbe seen that the instrumented treadmill 10, 10′ is operatively coupledto the programmable logic controller (PLC) 58 by the data transfer path82, which allows data to be transferred in both directions between theinstrumented treadmill 10, 10′ and the programmable logic controller(PLC) 58. For example, the treadmill control signals are sent from theprogrammable logic controller (PLC) 58 to the instrumented treadmill 10,10′, and feedback data in the form of belt speed, acceleration, andposition is sent from the instrumented treadmill 10, 10′ to theprogrammable logic controller (PLC) 58. Also, as shown in FIG. 10, theauxiliary input/output devices 68 are operatively coupled to theprogrammable logic controller (PLC) 58 by the data transfer path 84,which allows data to be transferred in both directions between theauxiliary input/output devices 68 and the programmable logic controller(PLC) 58. For example, as described above, the auxiliary input/outputdevices 68 of the system 100, 200 may be connected to the input/output(I/O) module of the programmable logic controller 58, which enables theauxiliary input/output devices 68 to be easily synchronized with therest of the system components (e.g., if one or more treadmill belttachometers are provided as auxiliary input/output devices 68, it isadvantageous to connect these devices to the PLC 58 so that they aresynchronized with the operation of the instrumented treadmill 10, 10′).Further, as illustrated in FIG. 10, it can be seen that the motion base52 is operatively coupled to the programmable logic controller (PLC) 58by the data transfer path 86, which allows data to be transferred inboth directions between the motion base 52 and the programmable logiccontroller (PLC) 58. For example, motion base control signals are sentfrom the programmable logic controller (PLC) 58 to the motion base 52,and feedback data in the form of motion base position, velocity, andacceleration is sent from the motion base 52 to the programmable logiccontroller (PLC) 58.

Also, as depicted in FIG. 10, it can be seen that data acquired by thecameras 50 of the motion capture system is transferred via the datatransfer path 88 to a data acquisition/data processing device (i.e.,computing device) with the motion capture software 80 loaded thereon. Asdescribed above, the motion capture software 80 is used to calculatejoint kinematics and kinetics using the data from the instrumentedtreadmill 10, 10′ and the motion capture system, and to identify gaitevents, such as heel strike. Referring again to FIG. 10, it can be seenthat data is sent from the programmable logic controller (PLC) 58 to thesystem integration software 75 via the data transfer path 90. The datapath 90 is used to transfer data from the firmware of the PLC 58 to thesystem integration software 75 so that the variables defined in thefirmware are capable of being accessed by the treadmill control softwareon the computer user interface (UI) of the instrumented treadmill 10,10′ using this protocol. In addition, as shown in FIG. 10, analog forcemeasurement data is sent from the instrumented treadmill 10, 10′ to thesystem integration software 75 via the data transfer path 92.Advantageously, the data paths 82, 90, 92 allow both analog data anddigital data to be collected from the instrumented treadmill 10, 10′ andto be delivered to the system integration software 75 simultaneously. Asdescribed above, the analog force measurement data acquired by thepylon-type force transducers 56 of the instrumented treadmill 10, 10′may be converted to digital force measurement data using ananalog-to-digital (A/D) board, and then converted to output load data bymeans of a data acquisition/data processing device (i.e., measurementcomputing device). If the researcher or clinician wants to use analogdata instead of digital data, the data path 92 enables the systemintegration software 75 to directly read the analog data from theinstrumented treadmill 10, 10′. Also, as illustrated in FIG. 10, dataprocessed by the motion capture software 80 is sent to the systemintegration software 75 via the data transfer path 94. The data path 94allows the marker data collected by the cameras 50 to be sent to thesystem integration software 75 for processing. This marker data is usedto calculate the joint kinematics and kinetics, which are synchronizedwith the force data from the instrumented treadmill 10, 10′, so that themovement of the subject is able to be displayed in real time on thespherical screen 31 of the visual display device 30 during a gait trial.

With reference once again to FIG. 10, it can be seen that data istransferred between the system integration software 75 and theuser-developed virtual reality interface software layer 78 (oruser-developed application software layer 78) via the data transfer path96. For example, the data is transferred between the system integrationsoftware 75 and the user-developed application software layer 78 bymeans of a motion management (MM) server. The MM server is the two-waycommunication protocol used for the data transfer between the systemintegration software 75 and the user-developed application software 78.Any data that is available in the system integration software 75 iscapable of being sent to the user-developed application software 78. Forexample, in the illustrative embodiment, the treadmill belt speed, thespeed scaling factor, the calculated output forces, and the center ofpressure (COP) is sent to the user-developed application software 78.The belt speed and speed scaling factor are used to control the opticflow at the same speed as the treadmill belts. The output forces andcenter-of-pressure (COP) may be simply displayed on the spherical screen31 in graphical form for biofeedback purposes (e.g., feedback displaycharts), or alternatively, may be used for any complex visual feedback,such as that used in animation. As described hereinafter, in someembodiments, the data transfer path 96 may be omitted when the forcemeasurement systems 100, 200 are provided with a separate virtualreality software dynamic-link library (DLL) layer. As an example, thebelt speed of the instrumented treadmill 10, 10′ may be transferred fromthe system integration software 75 to the user-developed applicationsoftware 78 so that the user-developed application software 78 may usethese parameters to set the speed of the optic flow. Conversely, asanother example, scene selection data may be transferred from theuser-developed application software 78 to the system integrationsoftware 75 if there are multiple scenes from which a user is able tochoose. In this example, a scene selection command is sent from theuser-developed application software 78 to the system integrationsoftware 75 so that a user is able to select, for example, differentground surface types in a virtual scenario or different levels ofdifficulty in a virtual scenario. In the illustrative embodiment, all ofthe variables in the virtual scenario are stored in the systemintegration layer 74 (e.g., ground surface type, etc.).

Also, as illustrated in FIG. 10, it can be seen that commands are sentfrom the user-developed virtual reality interface software layer 78 (oruser-developed application software 78) to the projector 40 of thevisual display device 30 via the data transfer path 98 so that the sceneimages generated by the user-developed application software 78 may bedisplayed on the spherical screen 31 of the visual display device 30.Turning again to FIG. 10, when a separate virtual reality software DLLlayer is provided, it can be seen that data is transferred between thesystem integration software 75 and the virtual reality software DLL 76via the data transfer path 102. More particularly, as shown in FIG. 10,data is sent from the system integration software 75 to the virtualreality software DLL 76 via the MM server, and from the virtual realitysoftware DLL 76 to the system integration software 75 via the MM server.In FIG. 10, it can also be seen that, when a separate virtual realitysoftware DLL layer is provided, data is transferred between the virtualreality software DLL 76 and the user-developed application software 78via the data transfer path 104. Like the data path 102 between thesystem integration software 75 and the virtual reality software DLL 76,the data path 104 between the virtual reality software DLL 76 and theuser-developed application software 78 also allows data to betransferred in both directions. When the force measurement systems 100,200 are provided with the separate virtual reality software DLL layer,the data paths 102, 104 may be used in lieu of the data path 96.

Finally, with reference again to the block diagram of FIG. 10, it can beseen that the system integration software 75 is capable of sending andreceiving signals to and from the auxiliary input/output devices 68 viathe data transfer path 106. For example, the system integration software75 may send and receive signals from the head movement tracking system,the treadmill belt speed measurement devices, the one or more inertialmeasurement units (IMUs), the galvanic stimulator and/or the handtrigger mentioned above. For example, when a hand trigger is provided asone of the auxiliary input/output devices 68 to the system 100, 200, thehand trigger may send a pulse to the system integration software 75,which can be used to mark events in the data set based on theresearcher's observations or clinician's observations. Advantageously,the auxiliary input/output devices 68 provide additional informationabout the movement of the subject, and also may enable various musclesof the subject to be activated (i.e., in the case of galvanicstimulator). For example, the head tracker is capable of determining theposition of the subject's head, while the eye tracker is capable ofdetermining the position of the subject's eyes. Also, when the output ofthese two devices is combined, the gaze direction of the subject iscapable of being determined. As another example, when electromyography(EMG) devices are provided as one of the auxiliary input/output devices68, information about the muscle activations of the subject are capableof being determined by the system 100, 200. As yet another example, whena foot switch is provided as one of the auxiliary input/output devices68, the foot switch may be used to indicate gait patterns of the subjector to trigger auditory feedback that is delivered to the subject. Asstill another example, when a galvanic stimulator is provided as one ofthe auxiliary input/output devices 68, signals may be sent to thegalvanic stimulator based on one or more gait events in order to triggera voltage to activate certain muscles of the subject. Advantageously,because the data transfer path 106 allows auxiliary input/output devices68 to be connected directly to the system integration software 75, thenumber of analog inputs to the programmable logic controller (PLC) 58 isable to be reduced as a result of the auxiliary input/output devices 68not all being required to be connected to the PLC 58.

Next, the closed loop biofeedback functionality of the illustrativeforce measurement systems 100, 200 will be described with reference toimmersive scenarios depicted in FIGS. 13-23. In the illustrativeembodiment, the control parameters of the instrumented treadmill 10, 10′may change in accordance with the scene that is being displayed on thespherical screen 31 of the visual display device 30. Also, auditoryfeedback may be provided to the subject while he or she is disposed onthe instrumented treadmill 10, 10′. In addition, the closed loopbiofeedback functionality of the system 100, 200 may have varying levelsof difficulty. Further, a head movement tracking system to measure thehead movement of the subject and/or an eye movement tracking system tomeasurement the eye movement of the subject may be utilized inconjunction with closed loop biofeedback functionality of the systems100, 200. Advantageously, the closed loop biofeedback functionality ofthe illustrative force measurement systems 100, 200 is capable of beingused with a diverse selection of subject populations (e.g.,adult/pediatric, healthy/pathological, etc.).

In an exemplary embodiment, the data acquisition/data processing device60 of the force measurement systems 100, 200 generates a scene imagewith a plurality of different ground surfaces (e.g., concrete, grass,sand, gravel, etc.). These scene images are then displayed on the on thespherical screen 31 of the visual display device 30 so that the sceneimages are able to viewed by the subject while he walks or runs on theinstrumented treadmill 10, 10′. In this exemplary embodiment, thecontrol variable is the treadmill belt speed and the output variable isthe number of miles traveled by the subject on the instrumentedtreadmill 10, 10′ (i.e., belt travel).

In the exemplary embodiment, the decreasing order of treadmill beltspeed for different ground surfaces may be as follows: (i) paved groundsurface—highest belt speed, (ii) grass ground surface—intermediate beltspeed, and (iii) sand or dirt ground surface—lowest belt speed. In theuser-developed application software 78, the variable “grd_surface” maybe associated with the type of ground surface that is being displayed onthe spherical screen 31 of the visual display device 30 to the subject.As the ground surface that is displayed on the spherical screen 31changes, the variable “grd_surface” is continuously updated in theuser-developed application software 78, and the values of the variable“grd_surface” are continually passed to the system integration software75 at the system integration layer 74. By means of communicating withthe instrumented treadmill 10, 10′ through the programmable logiccontroller 58, the system integration software 75 then continuallyupdates the treadmill belt speed based on the value of the variable“grd_surface”. For example, when the variable “grd_surface” is set to avalue “3” indicative of a paved ground surface, the treadmill belt speedmay be set to 2.0 meters per second (2.0 m/s). When the variable“grd_surface” is set to a value “2” indicative of a grass groundsurface, the treadmill belt speed may be set to 1.5 meters per second(1.5 m/s). Finally, when the variable “grd_surface” is set to a value“1” indicative of a sand ground surface, the treadmill belt speed may beset to 1.0 meters per second (1.0 m/s).

With reference to FIGS. 13-16, an immersive island pathway scene inaccordance with another illustrative embodiment of the invention will bedescribed. Initially, with reference to FIG. 13, it can be seen that theisland screen image 120 comprises a walking pathway with a rocky portion122 forming a portion of the pathway. The rocky portion 122 of theisland pathway represents a paved ground surface encountered by thesubject. When the subject walks across the rocky portion 122 of thepathway in the virtual island scene, the user-developed applicationsoftware 78, sets the variable “grd_surface” to a value “3” indicativeof a paved ground surface, which in turn, results in the treadmill beltspeed assuming its highest setting, as described above. Next, turning toFIG. 14, it can be seen that the island screen image 120′ comprises awalking pathway with a grassy portion 124 forming a portion of thepathway. When the subject walks across the grassy portion 124 of thepathway in the virtual island scene, the user-developed applicationsoftware 78, sets the variable “grd_surface” to a value “2” indicativeof a grassy ground surface, which in turn, results in the treadmill beltspeed assuming its intermediate setting, as described above. Then, withreference to FIG. 15, it can be seen that the island screen image 120″comprises a walking pathway formed from a combination of dirt and sand126. When the subject walks across the walking pathway comprising thecombination of dirt and sand 126 in the virtual island scene, theuser-developed application software 78, sets the variable “grd_surface”to a value “1” indicative of a dirt and/or sand ground surface, which inturn, results in the treadmill belt speed assuming its lowest setting,as described above.

As another exemplary scenario in the exemplary embodiment, the subjectmay be walking along on a paved or other surface type in the virtualenvironment displayed on the spherical screen 31 of the visual displaydevice 30, and then suddenly encounters a puddle of water on the walkingsurface. In this exemplary scenario, while the subject is crossing thepuddle, the treadmill belt speed is reduced. For example, in theimmersive island pathway scene of FIG. 16, the island screen image 120′″comprises a walking pathway with a puddle 128 disposed across a portionof the walking path. When the subject walks across the puddle 128 in thevirtual island scene, the treadmill belt speed is reduced. In order toimplement this reduction in treadmill belt speed, the user-developedapplication software 78 may set a Boolean variable “grd_puddle”continuously while the subject navigates through the virtualenvironment. This variable “grd_puddle” is continually received by thesystem integration software 75 from the user-developed applicationsoftware 78. If the variable “grd_puddle” set is set to “0”, thetreadmill belt speed is set at the current belt speed. However, if apuddle appears in the virtual environment, the variable “grd_puddle” isset to “1”, and this value is sent to the system integration software75. Then, by means of communicating with the instrumented treadmill 10,10′ through the programmable logic controller 58, the system integrationsoftware 75 reduces the treadmill belt speed by a predetermined amount(e.g., current treadmill belt speed of 2.0 m/s−0.25 m/s=1.75 m/s). In asimilar manner, the current belt speed of the instrumented treadmill 10,10′ may be reduced for an uneven surface or irregular rocky surface inthe virtual environment.

As yet another exemplary scenario in the exemplary embodiment, thesubject may be instructed to direct his or gaze at targets that willappear on the spherical screen 31 of the visual display device 30 (e.g.,the targets 136 in the immersive castle scene of FIGS. 17-23 that willbe described hereinafter). In this scenario, the subject may beoutfitted with a head tracker and/or an eye tracker in order to indicatethe gaze direction of the subject in order to determine whether or notthe subject is looking at the intended targets on the screen 31. Inaddition to, or as an alternative to the head tracker and/or eyetracker, the subject may be provided with a pointing device so that heor she is able to indicate the target direction by pointing to thetargets on the screen. In this exemplary scenario, the variables“target_reached” and “target_focus” may be maintained in theuser-developed application software 78, with both being set to values of“0” at the beginning of the subject testing or training routine. Thevalues of these variables are sent to the system integration software 75at the system integration layer 74. When a target appears on the screen31, the value of the variable “target_reached” is set to “1” in theuser-developed application software 78, and the position of thesubject's head and/or eyes is determined using the head tracker and/oreye tracker. Similarly, if the pointing device is used in addition to,or as an alternative to the head tracker and/or eye tracker, thepointing direction of the subject is determined. If the subject isdetermined to be gazing in the direction of the target and/or pointingat the target, the value of the variable “target_focus” is set to “1”,otherwise the value of the “target_focus” is set to “0”. If both thevariable “target_reached” is set to “1” and the variable “target_focus”is set to “1”, treadmill belt speed is set to, or remains at the currenttreadmill belt speed. Although, if the variable “target_reached” is setto “1” and the variable “target_focus” is set to “0”, the systemintegration software 75 reduces the treadmill belt speed by apredetermined amount (e.g., current treadmill belt speed of 2.0 m/s−0.25m/s=1.75 m/s). That way, the speed of the treadmill belt speed isreduced so as to make it easier for the subject to properly focus on theintended target.

In one or more embodiments, the intended targets that are displayed onthe spherical screen 31 of the visual display device 30 are not part ofa virtual keyboard on the screen 31 for controlling the operation of thetreadmill, wherein the virtual keyboard is intended to replace and/orsupplement the typical hardware-based treadmill control panel. Rather,as described hereinafter in the illustrative embodiment of FIGS. 17-23,the intended targets are objects in an immersive scene displayed on thescreen 31 of the visual display device 30, such as the targets 136described below.

With reference to FIGS. 17-23, an immersive castle scene in accordancewith yet another illustrative embodiment of the invention will bedescribed. Initially, with reference to FIG. 17, it can be seen that thecastle screen image 130 comprises a carpeted pathway portion 132 and atiled pathway portion 134. In the immersive castle scene, the subjectprogresses down the virtual pathway in the castle with the carpeted andtiled pathway portions 132, 134. The castle screen images of FIGS. 18and 19 are substantially identical to the castle screen image 130 ofFIG. 17, except that the screen image of FIG. 18 comprises a target 136disposed in the lower, left-hand corner of the scene image, while thescreen image of FIG. 19 comprises a target 136 disposed in the lower,right-hand corner of the scene image. Similarly, the castle screenimages of FIGS. 20 and 21 are substantially identical to the castlescreen image 130 of FIG. 17, except that the screen image of FIG. 20comprises a target 136 disposed in the upper, left-hand corner of thescene image, while the screen image of FIG. 21 comprises a target 136disposed in the upper, right-hand corner of the scene image. Inaddition, the castle screen images of FIGS. 22 and 23 are substantiallyidentical to the castle screen image 130 of FIG. 17, except that thescreen image of FIG. 22 comprises two (2) spaced-apart targets 136disposed at the top of the scene image, while the screen image of FIG.23 comprises two (2) spaced-apart targets 136 disposed in diagonallyopposite upper and lower corners of the scene image (i.e., in the upper,left-hand corner of the screen image 130 and in the lower, right-handcorner of the screen image 130). For example, in the immersive castlescene, the subject is instructed to direct his or her gaze towards, orpoint at one of the targets 136 in the scene image 130. In the immersivecastle scene, if the subject is determined to be gazing in the directionof the target 136 and/or pointing at the target 136, the treadmill beltspeed is set to, or remains at the current treadmill belt speed in themanner described above. However, if the subject is determined to begazing in an incorrect direction (i.e., in a direction not directed atthe target), the treadmill belt speed will be reduced by a predeterminedamount in the manner described above so as to make it easier for thesubject to properly focus on the target 136. When two (2) spaced-aparttargets 136 are disposed on the screen, as in FIGS. 22 and 23, thesubject may be instructed to gaze and/or point in the direction of thetargets 136 in succession. That is, initially the subject may be askedto gaze and/or point in the direction of the first target, and thensubsequently, the subject may be asked to gaze and/or point in thedirection of the second target. Also, similar to the immersive islandscene described above, the treadmill belt speed may be modified inaccordance with the ground surface type in the immersive castle scene ofFIGS. 17-23. For example, when the subject walks across the carpetedpathway portion 132 of the pathway in the castle, the user-developedapplication software 78, sets the variable “grd_surface” to a value “2”indicative of a carpeted surface, which in turn, results in thetreadmill belt speed assuming its intermediate setting, as describedabove. When the subject walks across the tiled pathway portion 134 ofthe pathway in the castle, the user-developed application software 78,sets the variable “grd_surface” to a value “3” indicative of a pavementsurface, which in turn, results in the treadmill belt speed assuming itshighest setting, as described above.

In the exemplary embodiment, when the motion base 52 is provided as partof the force measurement system 200, the motion base 52 may displace theinstrumented treadmill 10′ disposed thereon in accordance with the scenebeing displayed on the spherical screen 31 of the visual display device30. For example, if an inclined ground surface is being displayed in thescene, then the instrumented treadmill 10′ may be tilted by the motionbase 52 so that it assumes an inclined position corresponding to theinclined ground surface in the scene. As another example, if a collisionoccurs in the scene (i.e., walking into a wall, etc.), then the motionbase 52 may respond to the scene collision and/or the belt speed of theinstrumented treadmill 10′ may be reduced to zero in response to thescene collision.

In the illustrative embodiment, the data acquisition/data processingdevice 60 of the force measurement systems 100, 200 may generate twodifferent types of auditory feedback that is capable of being deliveredto the subject, namely discrete auditory feedback and continuousauditory feedback (sonification). Discrete auditory feedback is simplerto interpret for subjects with neurological disorders, but for some, itmay be so easy that their brain stops recognizing it. As such, in theillustrative embodiment, both types of auditory feedback are provided.For example, a discrete signal in the form of a beep or gong isdelivered to the subject after every mile that is traveled by thesubject on the instrumented treadmill 10, 10′. In this same example, thesonification feedback results in changing some sound parameter(rhythm/pitch) based on the movement, such as a background score withchanging rhythm and/or pitch as per change in belt speed.

As shown in FIGS. 1-6, in the illustrative embodiment, a pair ofspeakers 25 may be used to deliver the auditory feedback to the subjectdisposed on the instrumented treadmill 10, 10′. In the illustrativeembodiment, the left speaker 25 delivers auditory feedback to thesubject regarding the left side movement of the subject (e.g., auditoryfeedback regarding the movement of the subject's left leg), while theright speaker 25 delivers auditory feedback to the subject regarding theright side movement of the subject (e.g., auditory feedback regardingthe movement of the subject's right leg). As mentioned above, theauditory feedback may be in the form of a discrete signal and/or acontinuous signal. For example, a scenario using a discrete auditorysignal may involve a subject walking on the treadmill while the numberof miles traversed by the subject is tracked by the system 100, 200. Inthis scenario, a goal may be set for the number of miles (e.g., afterevery mile, a discrete auditory feedback in the form of a beep/gong orany other suitable sound may be emitted by the speakers 25). As anotherexample, a scenario using a continuous auditory signal may involve asubject walking on the treadmill in a self-paced mode (i.e., in theself-paced mode, the speed of the treadmill is consistently varied overtime in order to ensure that the subject is centered in a longitudinaldirection of the treadmill belt). In this scenario, a continuous soundis emitted by the speakers 25, but as the subject's speed changes,different parameters of the continuous auditory signal are modified,such as the volume or pitch of the sound.

Also, in the self-paced mode, the data acquisition/data processingdevice 60 may be programmed such that the optic flow is also self-paced.In particular, when the subject is walking through any scene on thevisual display device 30 in the self-paced mode, the optic flow is setbased on the speed of the treadmill 10, 10′ (i.e., the optic flow issynchronized with the speed of the treadmill 10, 10′). This way, theoptic flow is also self-paced and user-controlled.

The varying levels of difficulty in the exemplary embodiment may becreated by varying the belt speed of the instrumented treadmill 10, 10′.That is, the higher the level of difficulty, the greater the belt speed.Also, the belts speed of the instrumented treadmill 10, 10′ maycorrespond to different ground surface types displayed on the sphericalscreen 31 of the visual display device 30. For example, when a subjectis first beginning the testing or training routine, a scene containing astandard solid ground surface may be displayed on the spherical screen31 of the visual display device 30. During this initial part of thetesting or training routine, the treadmill belt speed is at a firstspeed setting (e.g., a low speed setting). Although, later in thetesting or training routine, a scene containing more challenging groundsurface, such as irregular gravel, may be displayed on the sphericalscreen 31 of the visual display device 30. During this latter part ofthe testing or training routine, the treadmill belt speed is at a secondspeed setting than is higher than the initial speed setting so that itis more challenging for the subject. Also, in the exemplary embodiment,certain treadmill speeds and certain ground surfaces may indicatedifferent levels of difficulty, which can be accessible only aftercompleting a predetermined number of miles on the treadmill. As anotherexample, the scene displayed on the spherical screen 31 of the visualdisplay device 30 may comprise one or more obstacles therein that becomeincreasing more difficult as the testing or training routine progressesover time (e.g., a virtual obstacle that is placed in front of thesubject may become larger with increasing levels of difficulty so thatit becomes increasingly more difficult for the subject to step over, ormaneuver around the obstacle).

In the exemplary embodiment, the head movement tracking system or theeye movement tracking system may be used an input device to selectdifferent paths in the scene on the spherical screen 31 of the visualdisplay device 30. For example, the subject may be given all three (3)of the following options for selecting a particular path in the visualworld: (i) remote control, (ii) head tracker, and (iii) eye tracker. Forexample, if the subject rotates his or her head to the left, the headtracker and/or eye tracker detects the left-pointing orientation of thesubject's head, and selects a path in the visual scene that correspondsto this left position (e.g., a path on the left side of the visualscene). As such, in these embodiments, the subject may navigate throughthe immersive scenario using the head tracker and/or eye tracker.

In one further embodiment, the data acquisition/data processing device60 (i.e., the operator computing device) generates a virtual realityenvironment with an avatar, and displays the virtual reality environmentwith the avatar on the spherical screen 31 of the visual display device30. For example, the immersive virtual reality environment may comprisea scenario wherein an avatar is shown walking along a bridge or down anaisle of a grocery store. The avatar image displayed on the screen 31represents, and is manipulated by the subject disposed on theinstrumented treadmill 10, 10′. The animated movement of the avatarimage on the screen 31 is controlled based upon the positionalinformation acquired by the motion capture system described above, aswell as the force and/or moment data acquired from the instrumentedtreadmill 10, 10′. In other words, an animated skeletal model of thesubject is generated by the data acquisition/data processing device 60using the acquired data from the motion capture system and theinstrumented treadmill 10, 10′. The data acquisition/data processingdevice 60 then uses the animated skeletal model of the subject tocontrol the movement of the avatar image on the spherical screen 31 ofthe visual display device 30. The avatar image is created on the screen31 by the data acquisition/data processing device 60 mapping the actualcoordinates of the testing or training environment into the virtualworld that is displayed on the screen 31.

In another further embodiment, the data acquisition/data processingdevice 60 (i.e., the operator computing device) may generate a screenimage with one or more visual perturbations, and display the screenimage with the one or more visual perturbations on the spherical screen31 of the visual display device 30. For example, in one exemplaryembodiment, the perturbation screen image may comprise a substantiallyblank screen that oscillates back-and-forth (i.e., shakesback-and-forth) so as to perturb the subject while he or she is disposedon the instrumented treadmill 10, 10′.

It is readily apparent that the embodiments of the force measurementsystem 100, 200 described above offer numerous advantages and benefits.First of all, the embodiments of the force measurement system 100, 200explained herein include an immersive visual display device 30 thatenables a subject being tested to become fully immersed in a virtualreality scenario or an interactive game. In addition, the embodiments ofthe force measurement system 100, 200 described above are capable offully immersing a subject in a virtual reality environment, yet compactenough to fit in typical building spaces.

Any of the features or attributes of the above described embodiments andvariations can be used in combination with any of the other features andattributes of the above described embodiments and variations as desired.

Although the invention has been shown and described with respect to acertain embodiment or embodiments, it is apparent that this inventioncan be embodied in many different forms and that many othermodifications and variations are possible without departing from thespirit and scope of this invention.

Moreover, while exemplary embodiments have been described herein, one ofordinary skill in the art will readily appreciate that the exemplaryembodiments set forth above are merely illustrative in nature and shouldnot be construed as to limit the claims in any manner. Rather, the scopeof the invention is defined only by the appended claims and theirequivalents, and not, by the preceding description.

The invention claimed is:
 1. A force measurement system, comprising: aforce measurement assembly configured to receive a subject, the forcemeasurement assembly including: a top surface for receiving at least oneportion of the body of the subject; and at least one force transducer,the at least one force transducer configured to sense one or moremeasured quantities and output one or more signals that arerepresentative of forces and/or moments being applied to the top surfaceof the force measurement assembly by the subject; at least one visualdisplay device having an output screen configured to at least partiallycircumscribe three sides of a torso of the subject, the at least onevisual display device configured to display one or more scenes on theoutput screen so that the scenes are viewable by the subject, whereinthe one or more scenes are configured to create a simulated environmentfor the subject, and wherein the output screen of the at least onevisual display device comprises a bottom edge and a top edge; one ormore data processing devices operatively coupled to the forcemeasurement assembly and the at least one visual display device, the oneor more data processing devices configured to receive the one or moresignals that are representative of the forces and/or moments beingapplied to the top surface of the force measurement assembly by thesubject, and to convert the one or more signals into output forcesand/or moments, the one or more data processing devices furtherconfigured to dynamically increase or decrease a speed of one or moredisplaceable components of the force measurement system in accordancewith a visual element of the one or more scenes that are displayed onthe output screen of the at least one visual display device while thesubject navigates through the one or more scenes of the simulatedenvironment on the output screen of the at least one visual displaydevice; wherein the visual element of the scene that is displayed on theoutput screen of the at least one visual display device comprises anobstacle disposed in a virtual walking path of the subject; and whereinthe one or more data processing devices are further configured todetermine whether a foot of a virtual representation of the subject onthe output screen clears the obstacle, and when the foot of the virtualrepresentation of the subject does not clear the obstacle, generate anddisplay a visual indicator on the output screen of the at least onevisual display device that is indicative of the height that the footmust achieve to clear the obstacle.
 2. The force measurement systemaccording to claim 1, wherein the at least one visual display devicecomprises a concavely shaped projection screen having a cylindricalmiddle portion, a spherical bottom portion, and a spherical top portion,the cylindrical middle portion being disposed above the spherical bottomportion and below the spherical top portion, the cylindrical middleportion having a continuous curvature between first and second opposedside edges of the concavely shaped projection screen, wherein thecylindrical middle portion of the concavely shaped projection screenresults in a focal region for a subject disposed on the forcemeasurement assembly, rather than any one single focal point, so that animmersion experience for the subject is substantially unaffected by aheight of the subject.
 3. The force measurement system according toclaim 2, wherein the concavely shaped projection screen comprises aplurality of screen sections that are attached to one another so as toform the overall screen.
 4. The force measurement system according toclaim 1, wherein the force measurement assembly is in the form of aninstrumented treadmill.
 5. The force measurement system according toclaim 4, wherein the force measurement system further comprises a motionbase disposed underneath the instrumented treadmill, the motion baseconfigured to displace the instrumented treadmill in one or moredirections.
 6. The force measurement system according to claim 1,wherein the output screen of the at least one visual display devicefurther comprises an overhanging top portion and a top cutout defining acutout footprint; and wherein the force measurement system furthercomprises a motion capture system operatively coupled to the one or moredata processing devices, the motion capture system comprising at leastone motion capture device configured to detect the motion of one or morebody gestures of the subject, and the at least one motion capture devicebeing disposed within the cutout footprint of the top cutout of theoutput screen of the at least one visual display device.
 7. The forcemeasurement system according to claim 6, wherein the at least one motioncapture device comprises a plurality of motion capture devices, a subsetof the plurality of motion capture devices being circumferentiallyspaced apart around the top cutout of the output screen of the at leastone visual display device, and the subset of the plurality of motioncapture devices being disposed within the cutout footprint.
 8. The forcemeasurement system according to claim 6, wherein the one or more dataprocessing devices are configured to adjust the one or more scenes onthe output screen of the at least one visual display device inaccordance with the detected motion of the one or more body gestures ofthe subject by the at least one motion capture device, wherein the oneor more body gestures of the subject comprise at least one of: (i) oneor more limb movements of the subject, (ii) one or more torso movementsof the subject, and (iii) a combination of one or more limb movementsand one or more torso movements of the subject.
 9. The force measurementsystem according to claim 8, wherein the at least one motion capturedevice comprises a plurality of motion capture devices, and theplurality of motion capture devices of the motion capture system are inthe form of a plurality of cameras, the plurality of cameras configuredto capture the motion of the subject.
 10. The force measurement systemaccording to claim 9, wherein a first subset of the plurality of camerasof the motion capture system are disposed above the subject, and whereina second subset of the plurality of cameras of the motion capture systemare disposed behind the subject.
 11. The force measurement systemaccording to claim 10, wherein the first subset of the plurality ofcameras of the motion capture system are attached to the output screenof the at least one visual display device or to a screen supportstructure that supports the output screen of the at least one visualdisplay device; and wherein the second subset of the plurality ofcameras of the motion capture system are attached to one of: (i) theoutput screen of the at least one visual display device, (ii) a screensupport structure that supports the output screen of the at least onevisual display device, and (iii) a camera mounting structure that isattached to the output screen of the at least one visual display deviceor to the screen support structure.
 12. The force measurement systemaccording to claim 1, wherein the top surface of the force measurementassembly is disposed above the bottom edge of the output screen of theat least one visual display device, and the bottom edge of the outputscreen of the at least one visual display device is spaced apart from afloor on which the at least one visual display device is supported byone or more screen support members, the one or more screen supportmembers being spaced apart from the top surface of the force measurementassembly that is configured to receive the at least one portion of thebody of the subject.
 13. The force measurement system according to claim1, further comprising an input device operatively coupled to the one ormore data processing devices, the input device configured to enable thesubject to select different navigation paths in the one or more scenesof the simulated environment on the output screen of the at least onevisual display device.
 14. The force measurement system according toclaim 13, wherein the input device that is configured to enable thesubject to select different navigation paths in the one or more scenesof the simulated environment on the output screen of the at least onevisual display device comprises an eye position tracking device or ahead position tracking device.
 15. A force measurement system,comprising: a force measurement assembly configured to receive asubject, the force measurement assembly including: one or moredisplaceable components, the one or more displaceable components havingone or more respective surfaces for receiving one or more respectivelimbs of the subject; and at least one force transducer, the at leastone force transducer configured to sense one or more measured quantitiesand output one or more signals that are representative of one or moreloads being applied to the one or more respective surfaces of the one ormore displaceable components by the subject; at least one visual displaydevice having an output screen, the at least one visual display deviceconfigured to display a scene on the output screen so that the scene isviewable by the subject; a pointing or gaze direction determinationdevice configured to determine a pointing direction or gaze direction ofthe subject, the pointing or gaze direction determination device beingexternal to the at least one visual display device; and one or more dataprocessing devices operatively coupled to the at least one forcetransducer of the force measurement assembly, the at least one visualdisplay device, and the pointing or gaze direction determination device,the one or more data processing devices configured to receive the one ormore signals that are representative of the forces and/or moments beingapplied to the one or more respective surfaces of the one or moredisplaceable components by the subject, and to convert the one or moresignals into output forces and/or moments, the one or more dataprocessing devices further configured to generate at least a firstvisual element and a second visual element, and to display the firstvisual element and the second visual element in the scene on the outputscreen of the at least one visual display device, the one or more dataprocessing devices additionally configured to control the displacementof the one or more displaceable components of the force measurementassembly in accordance with the first visual element of the scene thatis displayed on the output screen of the at least one visual displaydevice, the one or more data processing devices further configured todetermine a manner in which the subject interacts with the second visualelement of the scene and to adjust the displacement of the one or moredisplaceable components of the force measurement assembly based upon theinteraction of the subject with the second visual element during asubject testing or training routine, the second visual element of thescene that is displayed on the output screen of the at least one visualdisplay device comprising at least one virtual target, and the one ormore data processing devices additionally configured to determine themanner in which the subject interacts with the second visual element ofthe scene by determining when the pointing direction or the gazedirection of the subject, as determined by the pointing or gazedirection determination device, coincides with the at least one virtualtarget displayed on the output screen, and when the pointing directionof the subject does not coincide with the at least one virtual targetdisplayed on the output screen; wherein, when the pointing direction ofthe subject coincides with the at least one virtual target displayed onthe output screen during the subject testing or training routine, theone or more data processing devices are further configured to maintain acurrent speed of the one or more displaceable components of the forcemeasurement assembly; wherein, when the pointing direction of thesubject does not coincide with the at least one virtual target displayedon the output screen during the subject testing or training routine, theone or more data processing devices are further configured to decreasethe speed of the one or more displaceable components of the forcemeasurement assembly below the current speed of the one or moredisplaceable components of the force measurement assembly so as to makeit easier for the subject to properly focus on the at least one virtualtarget during the subject testing or training routine; wherein the firstvisual element of the scene that is displayed on the output screen ofthe at least one visual display device comprises an obstacle disposed ina virtual walking path of the subject; and wherein the one or more dataprocessing devices are further configured to determine whether a foot ofa virtual representation of the subject on the output screen clears theobstacle, and when the foot of the virtual representation of the subjectdoes not clear the obstacle, generate and display a visual indicator onthe output screen of the at least one visual display device that isindicative of the height that the foot must achieve to clear theobstacle.
 16. The force measurement system according to claim 15,wherein the force measurement assembly is disposed on a motion base, themotion base configured to displace the force measurement assembly in oneor more directions.
 17. The force measurement system according to claim15, wherein the force measurement assembly is in the form of aninstrumented treadmill and the one or more displaceable components arein the form of one or more treadmill displaceable elements of theinstrumented treadmill; and wherein the one or more data processingdevices are further configured to adjust a rotational speed of the oneor more treadmill displaceable elements in accordance with the firstvisual element of the scene that is displayed on the output screen ofthe at least one visual display device.
 18. The force measurement systemaccording to claim 17, wherein the first visual element of the scenethat is displayed on the output screen of the at least one visualdisplay device comprises a ground surface element; and wherein the oneor more data processing devices are further configured to dynamicallyincrease or decrease the rotational speed of the one or more treadmilldisplaceable elements in accordance with a type of the ground surfaceelement of the scene that is displayed on the output screen of the atleast one visual display device.
 19. The force measurement systemaccording to claim 17, wherein the one or more data processing devicesare further configured to dynamically decrease the rotational speed ofthe one or more treadmill displaceable elements when the virtualrepresentation of the subject on the output screen collides with theobstacle disposed in the virtual walking path of the scene that isdisplayed on the output screen of the at least one visual displaydevice.
 20. The force measurement system according to claim 19, whereinthe virtual representation of the subject on the output screen of the atleast one visual display device comprises an avatar controlled by one ormore body gestures of the subject as detected by the force measurementassembly and a motion detection system.
 21. The force measurement systemaccording to claim 19, wherein the one or more data processing devicesare further configured to compute a center of pressure for the subjectas a function of the output forces and/or moments determined from theone or more signals of the force measurement assembly, and to control amovement of the virtual representation of the subject on the outputscreen of the at least one visual display device using the computedcenter of pressure.
 22. The force measurement system according to claim15, wherein the pointing or gaze direction determination devicecomprises at least one of the following devices: (i) an eye positiontracking device configured to track a position of one or more eyes ofthe subject, (ii) a head position tracking device configured to track aposition of the head of the subject, and (iii) a pointing deviceconfigured to indicate an aiming direction of a body portion of thesubject.
 23. The force measurement system according to claim 22, whereinthe one or more data processing devices are further configured tocontrol a navigation of the virtual representation of the subject on theoutput screen of the at least one visual display device in accordancewith an output signal from at least one of the eye position trackingdevice, the head position tracking device, and the pointing device. 24.The force measurement system according to claim 15, wherein the at leastone virtual target that is generated by the one or more data processingdevices and displayed on the output screen of the at least one visualdisplay device comprises a plurality of targets spaced apart on theoutput screen of the at least one visual display device; and wherein theone or more data processing devices are further configured to determinewhether the subject sequentially points in respective directions of eachof the plurality of targets.
 25. The force measurement system accordingto claim 15, wherein, during the subject testing or training routine,when the pointing direction of the subject coincides with the at leastone virtual target displayed on the output screen, the one or more dataprocessing devices are further configured to set a target focus variableto a first value; wherein, during the subject testing or trainingroutine, when the pointing direction of the subject does not coincidewith the at least one virtual target displayed on the output screen, theone or more data processing devices are further configured to set thetarget focus variable to a second value that is different from the firstvalue; and wherein the one or more data processing devices are furtherconfigured to maintain the current speed of the one or more displaceablecomponents of the force measurement assembly when the target focusvariable equals the first value, and wherein the one or more dataprocessing devices are further configured to decrease the speed of theone or more displaceable components of the force measurement assemblybelow the current speed of the one or more displaceable components ofthe force measurement assembly when the target focus variable equals thesecond value.